diff --git a/packages/opencode/src/session/llm.ts b/packages/opencode/src/session/llm.ts
index dc89db409e87..f5d9b1b46d46 100644
--- a/packages/opencode/src/session/llm.ts
+++ b/packages/opencode/src/session/llm.ts
@@ -307,7 +307,17 @@ export namespace LLM {
         ...headers,
       },
       maxRetries: input.retries ?? 0,
-      messages,
+      messages: [
+        ...(input.model.api.npm === "@ai-sdk/anthropic"
+          ? system.map(
+              (x): ModelMessage => ({
+                role: "system",
+                content: x,
+              }),
+            )
+          : ([{ role: "system", content: system.join("\n") }] as ModelMessage[])),
+        ...input.messages,
+      ],
       model: wrapLanguageModel({
         model: language,
         middleware: [